Curable organopolysiloxane compositions that can be cured by a hydrosilylation reaction are used as protective coating agents for semiconductor elements in photo couplers, light-emitting diodes, solid-state image sensors, and other optical semiconductor devices. The protective coating agents of such semiconductor elements are required to exhibit no light absorption or scattering.
Curable organopolysiloxane compositions that are cured by a hydrosilylation reaction to form cured products with a high refractive index and optical transmissivity can be exemplified by the following: a curable organopolysiloxane composition comprising an organopolysiloxane containing silicon-bonded phenyl groups and silicon-bonded alkenyl groups, an organohydrogencyclosiloxane, and a hydrosilylation reaction catalyst (see Japanese Unexamined Patent Application Publication (hereinafter referred to as “Kokai”) Hei 08-176447); a curable organopolysiloxane composition comprising a liquid or solid organopolysiloxane with a viscosity of not less than 10,000 mPa·s at 25° C. containing silicon-bonded phenyl groups and silicon-bonded alkenyl groups, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, and a hydrosilylation reaction catalyst (see Kokai Hei 11-1619); and a curable organopolysiloxane composition comprising an organopolysiloxane having at least two alkenyl groups in one molecule and having silicon-bonded aryl groups, an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, and a catalyst in the form of a platinum complex of an aryl-containing organosiloxane oligomer (see Kokai 2003-128922).
However, cured products obtained by curing such curable organopolysiloxane compositions have insufficient adherence to substrates, the surface of the cured products is sticky and, as a result, dust and dirt easily adheres thereto, causing a drop in transmissivity, and in addition, their hardness is low, which makes them prone to scratching.
It is an object of the present invention to provide a curable organopolysiloxane composition that has excellent curability and, when cured, forms a flexible cured product having a high refractive index and optical transmissivity, high adherence to various substrates it comes into contact with in the process of curing, high hardness and slight surface tack, and a semiconductor device of superior reliability obtained using said composition.